1. Field of the Invention
The present invention relates to an image process apparatus for superimposing a sub image such as a text on a main image such as a TV image, a method for forming a sub image data packet, and a recording medium thereof.
2. Description of the Related Art
Conventionally, translated texts for movies, control and adjustment indications for TV remote control operations, and so forth are superimposed on main images by sub image process systems.
The sub image display systems can be roughly categorized as character code systems and bit map data systems.
In the character code type sub image process systems, as shown in FIG. 27, character data (for example, characters and patterns) stored in a character memory 80 are retrieved from a character generator 81 as character code assigned to characters. The character code is transmitted to a sub image display portion 83. The character code is temporarily stored in a sub image frame buffer 84 and then required characters are displayed. In this system, dedicated hardware such as the character generator 81 is required. Since data to be transmitted to a display portion is only character code, the amount of data to be transmitted and display time for display process can be reduced.
However, since only prepared characters are displayed, the applications for displaying sub images are limited. Thus, although this system is suitable for a sound volume control screen for a TV or the like, it is not suitable in other contexts, such as superimposed texts on movies.
On the other hand, in the case of the bit map data systems, since bit map data of sub images are directly transmitted to the display portion, the dedicated hardware that generates sub images corresponding to the character code is not required. In addition, since the shapes of sub images that can be displayed are not limited, the number of applications for displaying sub images is great.
However, the data rate of the bit map data systems is much higher than that of the character code system. Thus, it can be said that the bit map data systems have losses of data transmission time and display process time.
In other words, in the bit map data systems, each pixel should have sub image color data, sub image contour color data necessary for superimposing a sub image on a main image, and a mixing ratio of the main image and sub image. Thus, the data rate of data to be transmitted to the display portion becomes large.
In the bit map data systems, since pixel data with the same amount of data for one screen of a main image should be transmitted to the display portion, display spatial loss takes place. Hereinafter, the data for one screen is referred to as a frame.
In addition, in the bit map systems and the character code systems, even if the shape of a sub image that is being displayed does not change, sub image data should be continuously transmitted at each display frame interval. Thus, in data transmission and display control of these systems, there is temporal loss.
Consequently, in the above-described conventional sub image process systems, the bit map data system is superior to the character code system in effectiveness of generating sub images. However, the bit map data system has display spatial loss and temporal loss.